1. Field of the Invention
This invention relates to automatic steam traps of the type in which there is activation of a valve directly by a thermostatic element of the expanding fluid-filled type. In more general parlance, it relates to bellows-actuated thermostatic steam traps. More particularly, it relates to a trap of this character which has a dual modality of operation.
2. Description of the Prior Art
As is known to those skilled in this art, the purpose of a steam trap is to remove condensate and vent noncondensables from steam systems without losing any steam. The most efficient trap is one which accomplishes this under varying conditions of pressure and temperature.
Steam traps may be variously classified and differences of opinion exist as to the number of genre which exist and their names. For example, Gleason et al in U.S. Pat. No. 3,347,257 state that there are three general types (i.e. bucket, thermostatic or expansion, and thermodynamic). On the other hand, in "Hook-up Designs for Steam & Fluid Systems" (Sarco Company, Allentown, Pa. 7th ed - 1981, pg 16 et seq) five different types are described, namely, (1) balanced pressure thermostatic, (2) liquid expansion, (3) float and thermostatic, (4) inverted bucket and (5) thermodynamic. Each of these traps has its strengths and its weaknesses. Yet their mutual exclusivity works an economic hardship on the process plant which must stock various types for various applications.
Consider, for example, the fact that in a typical chemical process plant or oil refinery, there are two major important uses for steam traps. They are used in connection with steam tracing of product lines, which must be heated to keep their contents at desired temperature and/or viscosity. They are also used for draining condensate from steam mains. These two uses, however, require different operating characteristics. In the draining of condensate from steam mains, the condensate is removed at approximately saturation temperature even though it contains significant sensible heat. This is so because the presence of condensate is undesirable and, under some conditions, hazardous. In the draining of steam tracing lines, however, condensate is removed at temperatures well below saturation in order to achieve maximum utilization of sensible heat. Plants often stock balanced pressure thermostatic traps, for the first use and liquid expansion traps for the second use.
It would be desirable, therefore, to have a single trap which could perform functions traditional to both balanced pressure thermostatic traps and liquid expansion traps. By this it is not meant merely to have a common housing with interchangeable internals but, rather, a trap which is truly operable in a dual mode. In one of these modes, the trap would discharge condensate at a temperature close to saturated steam temperature. In the other of these modes, the discharge would be at a temperature significantly below saturated steam temperature.
The prior art in this field is legion. Still, U.S. Pat. No. 748,888 discloses a trap containing a diaphragm element and suggests inverting it to close the outlet instead of the inlet. There is no disclosure of what is achieved thereby. Smith et al, U.S. Pat. No. 1,467,818 is a conventional radiator trap, which uses a ball valve outlet and a bellows. In Oakley et al, U.S. Pat. No. 1,934,205 a trap is disclosed, which can be isolated for replacement of its thermostatic bellows. Irwin, U.S. Pat. No. 1,976,730 discloses a trap wherein blow off temperature can be adjusted over a wide range. However, despite the temperature setting, the valve still functions as a blow off trap. Smith, U.S. Pat. No. 2,229,529 controls flow of condensate in one direction and steam in another, by providing two mechanisms in a common housing. Clifford, U.S. Pat. No. 2,276,931 discloses a bellows which is unusually sensitive and requires less fluid than conventional devices. Morgan, U.S. Pat. No. 2,778,573 discloses a steam trap having a bellows and also a linked valve for providing two valving actions, if pressure increases. Reid et al, U.S. Pat. No. 3,725,989 discloses a steam trap, with a light metallic housing, which resembles embodiments of the instant invention. However, no dual mode of operation is disclosed. Further, tests have established that such traps are incapable of the requisite dual modality of operation. Beatty, U.S. Pat. No. 4,134,541 discloses a trap which combines a thermostatic bellows trap with a restrictive orifice in parallel. Cycling of the bellows, which is characteristic of blow traps, is reduced by the continuous condensate path through the orifice. Hetz, U.S. Pat. No. 4,288,032 provides a "universal" trap body into which can be placed various types of trap elements. While some of the above patents recognize the existence of the problem of need for dual applications, none postulates a solution as exemplified herein.
In addition to the foregoing prior U.S. patents, West German Offenlegungschrift No. 2,447,031 (filed Oct. 2, 1974; published Apr. 8, 1976) entitled "Condensate Trap", discloses a trap which includes a bellows having a valve member affixed thereto. By keeping the bellows immersed in a low pressure condensate reservoir, considerable freedom of trap location is stated to be achieved. However, there is no suggestion of a dual mode of operation in the context of the foregoing discussion. Bellows with valve members attached are also shown in Pamphlet 2E published by Spirax Sarco Limited, entitled "Spirax balanced-pressure thermostatic steam traps". Again, there is no suggestion of a dual mode of operation.